linux-kernel - Re: [PATCH 11/16] perf intel-pt: Add support for synthesizing callchains for regular events

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Message-ID: <20200417213704.GB21512@kernel.org>
Date:   Fri, 17 Apr 2020 18:37:04 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 11/16] perf intel-pt: Add support for synthesizing
 callchains for regular events

Em Fri, Apr 17, 2020 at 04:50:00PM +0300, Adrian Hunter escreveu:
> On 16/04/20 6:14 pm, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Apr 01, 2020 at 01:16:08PM +0300, Adrian Hunter escreveu:
> >> Currently, callchains can be synthesized only for synthesized events.
> >> Support also synthesizing callchains for regular events.
> > 
> > This is super cool, I wonder if we shouldn't do it automatically or just
> > adding a new type of callchains, i.e.:
> > 
> > 	perf record --call-graph pt uname
> > 
> > Should take care of all the details, i.e. do the extra steps below
> > behind the scenes.
> > 
> > Possibly even find out that the workload specified was built with
> > -fomit-frame-pointers, that the hardware has Intel PT and do all behind
> > the scenes for:
> > 
> > 	perf record -g uname
> > 
> > Alternatively we could take some less seemingly far fetched approach and
> > make this configurable via:
> > 
> > 	perf config call-graph.record-mode=pt
> > 
> > What do you think?
> 
> Adding a --call-graph option sounds reasonable, and config to define default
> callgraph options.  But this was done at Andi Kleen's request, so he may
> want to comment.

Andi? My concern is that if this is the optimal solution for a good
subset of the machines out there, then we need to make it easy to use,
even transparent, if possible and safe to take that path.

- Arnaldo